Reverting call circuit



Feb. 10, 1953 F. A. MORRIS 16 Sheets-Sheet l INVENTOR. FRANK/1. MORRIS ATTORNEY F. A. MORRIS REVERTING CALL GIRCUIT Original Filed June 21, 1949 Feb. 10,1953

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16 Sheets-Sheet 3 INVENTOR. FRANK A. Mom/s 411' ORA/E Y F. A. MORRIS REVERTING CALL. CIRCUIT FSw.

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Feb. 140, 1953 F. A. MoRRls 2,623,281

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A T TOR/YE Y Feb. 10, 1953 F. A. MORRIS REVERTING CALL-CIRCUIT l6 Sheets-Sheet 5 Original Filed June 21, 1949 IN V EN TOR. FRANK A. MORE/S 555 we 1a.

Feb. 10, 1953 F. A. MORRIS 2,628,281

REVERTING CALL CIRCUIT Original Filed June 21, 1949 16 Sheets-Sheet 6 I I l I I I I l I l l I I I I I N V EN TOR. FRANK A MORRIS $55 BY F 14 J 4 TTORNE Y Feb. 10, 1953 F. A. MORRIS REVERTING CALL CIRCUIT l6 Sheets-Sheet '7 Original Filed June 21, 1949 S w M F INVENTOR.

FRANKAMORR/S A 7' TORNE'Y Feb. 10, 1953 F. A. MORRIS 2,528,231

REVERTING CALL CIRCUIT Original Filed June 21, 1949 1e Sheets-Sheet 8 CPA CRT C8 C50 CCT CON 7v commas OFRELAYS aw! AND mp2 (/76. M.)

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FRANK A. MORRIS A TTORNEY Feb. 10, 1953 F. A. MORRIS REVERTING CALL CIRCUIT l6 Sheets-Sheet 9 Original Filed June 21, 1949 70 X Bfl/YA x FINDER SWITCH INVENTOR. FRANK A. Mom/s ATTORNEY F. A. MORRIS REVERTING CALL CIRCUIT Feb. 10, 1953 16 Sheets-Sheet 10 Original Filed June 21, 1949 INVENTOR. FRANK A. MORRIS ATTORNEY Feb. 10, 1953 F. A. MORRIS REVERTING CALL CIRCUIT 16 Sheets-Sheet 11 Original Filed June 21, 1949 INVENTOR. FRANK A. MORRIS A TTORNEY Feb. 10, 1953, F. A. MORRIS REVERTING CALL CIRCUIT l6 Sheets-Sheet 12 Original Filed June 21, 1949 A'PA ALs 6EEF/6.6.

INVENTOR. FRANK A. Mann/s 4rr0nwsr Feb. 10, 1953 M R 2,628,281

REVERTING CALL CIRCUIT FRANK A MORRIS A TTORNEY Feb. 10, 1953 F. A. MORRIS REVERTING CALL CIRCUIT l6 Sheets-Sheet 14 Original Filed June 21, 1949 5 s M MR T0 M E 0 VA R A m m e c I I I I l I I I I I l I III R V p l 5 R a E w 1 s I I I I 1 I I I I I I I 1 1 1 1 I I w .N\ \NQQQWH\ B m lllll 1| ATTORNEY Feb. 10, 1953 F. A. MORRIS REVERTING CALL CIRCUIT Original Filed June 21, 1949 16 Sheets-Sheet 15 INVENTOR. FRA/VKAMORR/S ATTORNEY 2250 218 P150 P15 PPT 7O FREQUENCY GFNEPA 709$ Patented Feb. 10, 1953 UNITED STATES PATENT OFFICE REVERTING CALL CIRCUIT Frank A. Morris, Rochester, N. Y., assignor to Stromberg-Carlson Company, Rochester, N. Y., a corporation of New York 4 Claims. 1

The present invention relates to telephone systems and more particularly to reverting call party line circuits for use in automatic telephone systems.

This is a division of my co-pending application Serial No. 100,373, filed June 21, 1949, which in turn is a division of my co-pending application, Serial No. 743,415, filed April 23, 1947, and each of which is assigned to the same assignee as the inventions described herein.

It is an object of my invention to provide a new and improved multi-party telephone system incorporating new and improved reverting call circuits.

GENERAL DESCRIPTION In accordance with my invention, there is provided a system employing step-by-step switches for line finding, each line finder being directly associated with a selector to form a finderselector link or combination. There is illustrated herein a 1000-line system and there is provided a suitable number of finder-selector links, as twenty, for example. There is provided an allotting circuit for pro-selecting an idle link for the next initiated call. In order to increase the rate of handling calls, the allotter has duplicate relays for all functions, thereby constituting a dual allotter in which each half is normally brought into action by half of the lines, there being, for example, 50 lines assigned to each allotter. Provision is made for transferring all the lines to one-half of the allotter under certain conditions.

After the line finder-selector link has selected the calling line, the selector is caused tohunt, upon the dialing of the first digit of the called number, to select an idle connector in that group of connectors designated by the first digit. After selection of the connector, second and third digits are transmitted to cause the connector step-bystep switch to move to a position corresponding to the called subscriber.

Line circuit.--In connection with a system such as that described herein, there is provided a line circuit at the terminating, as well as at the originating, end of each call. The line circuitsare arranged to supply ground over a start lead to initiate operation of the allotter; to mark the position of the calling line in the banks of the finder step-by-step switch; to transmit all links I busy tone to a subscriber when all of the finderselector links are in use; to transmit coin box tone to a manual operator when the system is so arranged; to prevent the indefinite holding of a line finder and selector combination when a perma- Divided and this ap- Line finder.-The line finder, as indicated above, is employed to find the calling line. In addition to this primary function, the line finder is used to attach the tip and ring conductors or leads to the calling line; to conduct a busy test to prevent cutting through metallic connections if a condenser has seized the calling line during the process of line finding; to cut tip and ring conductors .through to the connector on a metallic basis if the busy test is successful; to recycle the allotter if the line finder fails to stopin either direction of motion of the step-by-step switch; to provide trunk call identification to succeeding circuits; and to provide direct control of all links busy and link test marking paths to the allotter. The line finder may be provided with means for discriminating restricted levels in the selector and timed calling levels.

AZZotter.-The dual alotter, as stated above, serves primarily to control the operation of a pre-selected line finder and to pre-select another idle link upon completion of a line finding operation. The allotter is also used to pre-impulse the selector associated with the idle line finder when the allotter is energized; to drive the line finder in whatever direction is necessary to attach the finder-selector link to the calling line; to drive the line finder in one direction only to attach the link to a calling trunk as distinguished from a calling subscribers line; to recycle if the line or trunk is not found within a prescribed time; to transfer functions so that one side of the allotter can carry the entire load of the line group in case of trouble or in case all links normally served by the other side become busy; to operate peg count meters; and to return the all links busy tone when required.

SeZector.--The purpose of the selector circuit, as indicated previously, is to select a group of connectors under the direction of the dial and hunt automatically for an idle trunk in that group. In order to accomplish its purpose, the selector is caused to repeat the dial pulses received from the calling party in order to select the desired group of connectors, to hunt in the selected group for an idle trunk in the level selected by the dial, and then to establish a connection to the succeeding switching equipment. There may also be provided provisions for digit canceling, digit adding, permanent time release and the transmission of link idle and link busy indications to the allotter.

Connector.-The primary functions of the connector are to select a subscriber line and to establish ringing of the desired called station under the control of the calling party. The connector may be of various types depending upon the kind of service which it may be called upon to perform, such as party line ringing of either the harmonic or code type, P. B. X trunk hunting, conversation timing from one or both ends of the system, and revertive calling.

P. B. X trunk hunting allows the assignment of successive numbers to a business establishment, or the like, whose telephone needs are sufficiently great to justify the assignment of two or more consecutive telephone lines, in which case, the connector tests the lines in succession until a free line is found. Normally, when the first line is called, testing begins over the entire group. Provision may be made, as for night service, for example, such that if any line other than the first in the group is called, that line only is tested. This feature allows the listing in the telephone directory of all telephone lines, except the first, as night lines for particular individuals whereby at such times they receive the benefit of individual line service. Further objects and advantages as well as a detailed understanding of my invention will be apparent from a study of the following description when read in connection with the drawings in which Fig. 1 illustrates the basic features of a step-by-step switch which may be used to carry out the principles of my invention, Fig. 2 is a chart showing the relationship of the various figures of the drawings and which enables a complete wiring diagram to be as sembled if the various figures of the drawings are placed in the indicated locations, Fig. 3 illustrates the line circuit of my system, Fig. 4

depicts the finder switch and associated circuits,

Figs. 5 and 6 illustrate the various component parts of a selector embodying the principles of my invention, Figs. 7 and 8 and 9 show a connector circuit illustrating the principles of my invention, Fig. 10 shows a terminating line circuit, Figs. 11, 12 and 13 illustrate a dual allotter for use in the system described herein, Fig. 14 illustrates equipment which is common to the system, Figs. 15 and 16 illustrate an alternative reverting call circuit and Figs. 17 and 18 illustrate modifications of features of the circuits shown in Figs. 4, 11 and 12 and Figs. '7, 8 and 9 respectively. I

With respect to Figs. 5 and 6 relating to the selector, it is desired to point out that if permanent timing lock-out is to be employed, the equipment within the dashed rectangle marked with the numeral B is used, but if the look-out feature is not desired, the ground connection indicated within the dotted rectangle C is substituted. Attention is also called to the dashed rectangle D which is used if digit adding functions are required, in which case wiring M is used. If digit adding is not employed, rectangle D is omitted and wiring N is substituted.

Referring to the connector, illustrated in Figs. 7, 8, and 9, a number of alternative provisions are made. If directory number revertive calling i employed, the apparatus shown within the dashed rectangle E and D, W, and X wiring is used, but if the special revertive call circuit illustrated in Figs. 15 and 16 is furnished, the parts shown within rectangle E are omitted and D," W and Y wiring is used. If the trunk hunting feature is utilized, the parts shown in rectangle F are included and wiring C is used instead of D. If dual timing is made part of the system, wiring D is used, but if this service is not provided, wiring W is used. If conversation timing is furnished, wiring V is used in place of wiring W."

Step-b -step switch It is believed that a complete understanding of the principles of my invention requires not only an explanation of a complete telephone system, but also a description of a suitable stepby-step switch. There is illustrated in Fig. l, a switch specially adapted for use in the system embodying my invention and known by the trade name XY switch. This switch derives its name from the fact that the wipers or contact brushes, during movement to a desired position, traverse first in a primary direction and then in the same plane but in a secondary direction at right angles to the first direction, which, in the right-hand rectangular co-ordinate system are X and Y directions, respectively.

There is provided a carriage I, which makes the primary and secondary stepping movements and has a set of contact brushes comprising two pairs of wipers 2 and 3 mounted on it for tip, ring, sleeve and hunt connections, respectively. These wipers are bifurcated, employing twin contacts that make connection directly onto bare wires which run in banks behind the switches. The bare Wires may be arranged in molded frames which may be rigidly mounted to the cells which in turn hold the switches.

The carriage is driven by the cog roller 01 tubular shaft assembly 4 which slides along the shaft 5 during the X motion. The cog roller 4 is shown in the form of a double-cut tubular gear with ratchet teeth cut parallel to its length and rack teeth out as rings. The annular rack teeth mesh with and are driven in the X motion by a suitable sprocket or gear 6. For stepping in the X direction, the X magnet I, located in the upper left corner of the plate 8, operates, through a pawl 9, the ratchet wheel to which is suitably mounted on the sprocket assembly. In response to repeated pulses the magnet 1 steps the cog roller assembly 4 alon the shaft 5, positioning the wipers on the carriage l successively before each wire bank. Since four wipers are involved and each wiper has its own set of 11 wires, 44 rows of wires each 11 deep are lined up along the front edge of the mechanism plate, immediately before the wipers (see Fig. 4). The eleven pairs of wires that are lined up before a pair of wipers constitute a wire bank.

The XY switch is nominally a point switch, i. e., is normally given ten steps in the X direction and ten steps in the Y direction, thereby making possible the selection by the wipers, of any one of 100 lines.

To mark the level of X travel, for finder operation, timing or discriminatory purposes, an auxiliary set of contact brushes adapted to be positioned according to the position of the primary movement or set of brushes, and indicated by the numerals H and Ho, enters a sep rate bank comprising X and XX levels. Wipers I i and I la are operated by a pinion I 2 assembled with the sprocket 6 through a rack [3 to which it is attached. Thus, as the X magnet steps the sprocket 6, both the cog roller 4 and wiper rack 13 move, roller 4 to the right and rack l3 upwardly, as viewed in the drawing. When the X wiper i i has found the proper level, thereby positioning the wipers on the carriage before the proper wire banks, the X magnet I is deenergized and the Y magnet 15 takes over. The Y magnet I5 is located in the lower central portion of the mechanism plate. In stepping, its pawl It operates directly on the ratchet teeth of the cog roller 4, turning it, and thus driving the wipers 2 and 3 into the wire banks through the interaction between rack 29 and pinion 2|.

The X position of the wipers is shown by reference to a scale I? attached to the mechanism plate and the Y position by reference to a numbered drum 18 located on the tubular shaft assembly. Thus, the position of the wipers is determined directly and quickly.

It should be recognized that the momentum of the switch, if not arrested, would carry each step beyond its limits. This is more easily realized when one considers that the stepping is of the order of fifty per second. In order to stop the X motion at each step, the end of the armature 35 of the X magnet engages a tooth of the sprocket at the bottom point of the armature travel. The sprocket motion is, therefore, locked each time the X magnet completes a pulse.

In the Y motion, a cam (not shown) on the underside of the Y armature operates against a member 22 called the stop bar. This stop bar is rocked forward at each downward stroke of the Y armature. A knife edge on the stop bar 22 engages a ratchet wheel 23 on the end of the cog roller 4 locking the rotation of the cog roller, and thus the advancement of the wipers, at the completion of each Y armature stroke.

There are provided X oif-normal contacts or switches 25, Y off-normal contacts or switches 26, over-flow contacts or switches 21 and release springs or switch 28.

The off-normal and overflow switches are mounted as a common assembly located in the lower left-hand corner of the mechanism plate and the release springs are mounted on a separate assembly located near the release magnet 33.

The X and Y off-normal springs 25 and 26, respectively, perform similar functions, that of informing the relay equipment associated with each switch as to the position of the brushes or wipers. Operation of the X elf-normals, for instance, indicates that the switch has taken at least a single step in the X direction. Operation of the Y ofi-normals similarly indicates that at least a single step has been taken in the Y direction.

The circuit function of the off-normals differs in each use of the switch but, in general, indicates that it has either moved in one direction and should now move in another or all necessary motion has taken place. There is, however, one circuit function common to all switches and that is to remove current from the release magnet 30 when the brushes have returned to the normal position. When the release signal is given, current is kept on the release magnet 30 until the switch is fully home and is then removed to avoid unnecessary current flow and heating. Both the X and Y off-normals are used in this function since the switch can be moved independently in either direction.

In the event of certain incorrect manipulations or an all-trunks-busy condition, hunting switches may progress the entire length of the bank without encountering a stopping signal. Unless some means of correction were provided, they would continue to hunt vainly until the circuit was deenergized. Overflow springs 21, arranged to operate in the extreme position of the brushes in either the X or Y directions (namely the eleventh X or Y step), interrupt the magnet current in order instantly and permanently to stop useless stepping until the switch is released.

The release springs 28 have two important functions in connection with the release of the switch. First, it is necessary to continue the re complished by a release spring contact establishing a self-locking electrical circuit which keeps the driving pawls 9 and is removed from the ratchet wheel (X motion) and the cog roller (Y motion). The lock is interrupted when the switch returns home. The second function is performed by a second release spring which maintains a busy indication until the switch is home, thus preventing its seizure until everything is normal. When the release magnet 30 is energized, stop members 3| and 32 are removed from engagement with cog roller 4 and sprocket I0, respectively, through operation of armature 33. The Y return movement of the carriage is then performed by a spring 34 coiled in the tubular shaft of. the cog roller and the X movement by a spring (not shown) coiled around the shaft of the sprocket 5.

DETAILED CIRCUIT DESCRIPTION In the following detailed description, 9. call is traced from the calling party's station to the called partys station. Revertive calling is then discussed and finally circuit refinements to provide special features and to take account of special conditions are described.

The telephone system herein described in detail comprises a single selector and, therefore, serves a 1000-line system and requires the transmission of four digits, one to select the desired group of connectors, the second to determine the tens digit of the called number, the third to select the units digit of the called number, and the fourth to ring the called line. The principles of my invention, of course, are not limited to the particular choice of circuits described herein as a system and my invention is equally applicable to any desired combination of the various circuit components.

In describing the circuits involved, the various relays are designated by letter combinations. The first letter indicates the part of the system in which the relay is located, i. e., L indicates line circuit, F indicates finder, A indicates allotter, S indicates selector, C indicates connector, R indicates a special reverting call circuit and B refers to common equipment. Following the initial letter are one or more letters which are usually the initials of the name of the relay with which they are associated and which serve to identify that relay. For example, C refers to a calling relay, PT to a permanent timing relay, D to delay, and X and Y to switch motion. Thus, SXD refers to a slow release (delay) relay associated with the X motion of the selector switch. The relay contacts and armatures are identified by the same letters referred to above followed by a hyphen and then a numeral. Thus, SXD-Z designates an armature of the SXD relay.

It may be noted that in the described system, when the battery is connected into the system but no calls are being made, the ALB and ALI relays are energized but all other relays are de-energized. The ALB and ALI relays remain energized as long as there is an idle link (a link comprising a finder and a selector). The other relays are energized at various times during the progress of a call. Hence, in the drawings, the armatures of the ALB and ALI'relays are shown in the oper- 7 ated positions While the armatures of the rest of tery when used in the following circuit description refers to the negative side of battery. The positive side of battery is grounded and hence the term ground refers 'to positive battery.

Line circuit Referring to Figure 3 of the drawings, a call is initiated by removing the receiver from the hookswitch or cradle, thereby closing the hookswitch contacts 41 :as shown in Fig. 3 and completing a circuit through a suitable dialing mechanism 42 to the tip and ring leads, T and B, respectively. Closure of the hookswitch'completes a circuit for the energization of line relay LL. Relay LL is a two-winding relay. One terminal of the lower winding is connected-to battery and the other terminal is connected to the ring lead It through contact LCD-1i and armature LCD-3. The circuit to ground from the tip lead T coinprises armature LOO-.1, contact LCO-lthe other coil of relay LL, contact LLO-i and armature LLO-E to ground. If all-links-busy tone is to be provided, the foregoing circuit is grounded through a transformer as indicated in dashed lines in Fig. 3 instead of directly as shown by the solid line.

Gperation of line relay LL grounds a start lead LST to the dual allotter in order to cause a pre-selected finder to hunt for the calling line,

the line finder switch FSw corresponding to the calling line. The hunt lead H is grounded as follows: ground at armature LL-3, contact LL-t, armature 'l-LO-H, and contact LLO-I2, to the contact in the hunt bank of the line finder-corresponding to the calling line.

Ground on the start lead is utilized to operate a start relay-in the allotter (Figs. 11,12 and 13) which initiates the energization of the line finder switch (Fig. 4) chosen by the allotter to serve -1e call. The start lead is traced over the following circuit: ground at armatureLL-l, contact LL-E, armature LLO-fi, contact LLO-E, resistor 23, and start lead LST, to the allotter.

When the calling line is found, as will be more fully described hereinafter, ground is placed on the sleeve lead S in the sleeve bank of the finder switch FSw (Fig. 4) and conducted to the ime circuit by lead S. Presence of ground on the sleeve lead S operates the-cut-off relay LCO over circuit extending from grounded sleeve lead 8, armature LLod-contact LLB-9, winding-oi cut-o1? relay LCD to battery. If provision is made for the transmission of coin box tone to an operator, the cut-off relay LCD is connected to battery through-a transformerwinding as indicated in dotted lines in Fig. '3 instead of directly as shown by the solid line. Cut-off relay LCO locks up through a circuit extending from grounded sleeve lead S, through contact LCD-9, armature LCD-8, and winding of relay LCD to battery. Operation of the cut-oii relay is now independent of subsequent operation of lock-out relay LLO.

When the cut-chi relay'LCO is;energized, the

tip andring leads, T and R, respectively, are

disconnected from the line relay LL by the opening of the line circuit at contacts LCO-Z and LOO- i. De-energization of relay LL removes ground from the marking leads at contacts LL-2 and LL- i respectively.

The energization of cut-off relay LCO also causes ground to be placed on the winding of lock-out relay LLO, the circuit extending from the grounded sleeve lead S through contact LCO-S and armature LCO-S to one terminal of the winding of relay LLO. The other terminal of the LLO coil is connected to battery. Operation of the lock-out relay LLO breaks the original energization path tothe cut-off relay LCO at contact LLO-9 but the cut-01f relay LCO remains locked up as explained-above. Lock-out relay LLO locks up to the grounded sleeve lead S through its own armature LLO-B and contact LLO-l and hence is independent of any subsequent'acticn of cut-off relay LCO.

Allotter and Zinc finder In the at rest condition of the allotter, i. e., circuits connected but no calls being made, the allotter is cut through to an idle link comprising an interconnected finder and selector by means of contacts and brushes of the rotary link selector switch ALS. The link busy relays ALB and ALB associated with left and right hand portions, respectively, of the allotter and the link idle relays ALI and A'LI are normally picked up by grounds derived through chains of contacts in the line finder and the selector. Thus, referring to relay ALB (see Fig. 12), one side of its winding or coil is connected to battery. The other side of the coil ALB is connected to ground over a circuit extending through contact DK-l and arm DK-Z of the disable key DK, armature AS2-l8 and contact A'S2-i9 of start relay A'SZ, ALB lead to the finder (Fig. l), armature FYon-3 and contact FYon-t of the finder Y ofi-normal switch FYon, contacts of the make busy switch FMB, ALB lead from the finder to the selector (see Figs. '5 and 6), armature SYon-l and contact SYon-Z of the selector Y off-normal switch SYon, conductor 33, contact SD-B andarmature SD- i of selector delay relay SD, and contacts of the selector make busy switch SMB to ground. Inasmuch as all finder-selector links are multiplied, if any link is not operated or employed, relay ALB is energized through at least one closed oft-normal contact in the finder and the selector.

The operating circuit for link idle relay ALI is as follows: battery, upper winding of ALI, armature APT-i and contact APT-2 of the Permanent Timing relay APT, armature AS2-4, con tact AS2-3, arm and contact of rotary switch elementfiii of link selector switch ALS, link idle lead FLI to the line finder (Fig. 4), spring or armature FYon-i': and contact F-Yon-S of the finder Y cit-normal switch FYon, armature FZ-I and contact FZ-Z of release magnet FZ, armature and contact of make busy switch FMB link idle lead LI to the selector, contacts of the selector makebusy switch SMB, contact SYon-S, spring or armature SYon-4 of the selector Y off-normal switch 'SYon, contact SZ-I and armature SZ-Z of release magnet SZ to ground. In order to make link idle relay ALI pick up as rapidly as possible and insure halting of allotter cycling upon reaching an idle link, a second or lower winding is provided for relay ALI which is connected in parallel with the upper winding through armature ALI-l and contact ALI-2. When the .relay ALI picks up, the parallel circuit is broken .atcontact ALL-2. 

